Production of chlorinated phenols of improved color

ABSTRACT

Polychlorinated phenols (e.g., pentachlorophenol) of improved color are made by vacuum distilling polychlorinated phenols containing dark color-forming impurities in the presence of a color inhibitor such as zinc dust or free radical-acting substances (e.g., free radical-acting compounds of the phenol, hydroquinone, organic sulfur derivative, organic phosphite, amine and aldehyde type). Ethylene thiourea or zinc dust appear to offer an optimum combination of improved color, cost and process efficiency and are therefore the preferred color inhibitors. In addition, the chlorodioxin content of the impure pentachlorophenol (generally about) 2,000 p.p.m.) is reduced to a residual chlorodioxin content of less than 25 p.p.m. during distillation.

United States Patent [191 Christena [451 Sept. 30, 1975 1 PRODUCTION OFCHLORINATED PHENOLS OF IMPROVED COLOR [75] Inventor: Ray C. Christena,Wichita, Kans.

22 Filed: Nov. 9, 1973 211 Appl. No.: 414,533

[52] US. Cl. 203/6; 203/29; 203/32; 203/38; 260/623 R; 203/50; 203/91[51] Int. CI."...B01D 3/34; C23F 1l/00;C23F 14/00 [58] Field of Search260/623 R. 623 H; 203/6, 203/29, 38. 91, 32. 50

3.770.835 11/1973 Garabedian 260/623 R OTHER PUBLICATIONS Biltz et a1.,Berichte, 37. 4017. 4018( 1904).

Primary E.\'aminerNorman Yudkoff Assistant E.\'aminerFrank SeverAttorney, Agent. or Firm-Burns. Doanc. Swecker & Mathis 1 5 7 1 ABSTRACTPolychlorinated phenols (e.g.. pentachlorophenol) of improved color aremade by vacuum distilling polychlorinated phenols containing darkcolor-forming impurities in the presence of a color inhibitor such aszinc dust or free radical-acting substances (e.g.. free radical-actingcompounds of the phenol, hydroquinone. organic sulfur derivative.organic phosphite. amine and aldehyde type). Ethylene thiourea or zincdust appear to offer an optimum combination of improved color. cost andprocess efficiency and are therefore the preferred color inhibitors. 1naddition. the chlorodioxin content of the impure pentachlorophenol(generally about) 2,000 p.p.m.) is reduced to a residual chlorodioxincontent of less than 25 ppm. during distillation.

5 Claims, N0 Drawings OF CHLORINATED Pl-IENOLS OF IMPROVED COLORBACKGROUND OF THE INVENTION For some time it has been recognized thatphenol, especially when produced by the cumene process or by sulfonationof benzene, inherently contains some impurities which upon chlorinationof the phenol give rise to objectionable color formation. See, forexample, U.S. Pat. No. 2,864,869. Such impurities are present even inphenol which is U.S.P. grade, and are thought not to be separable fromthe phenol by ordinary fractional distillation. See, U.S. Pat. No.3,029,292. Hence, a number of techniques have been developed for thepurification of phenol which involve contacting the phenol with somechemical agent or heat treating it in the presence of a catalyst andthereafter recovering the phenol by fractional distillation. See, forexample, U.S. Pat. Nos. 3,102,149 and 3,029,293 as well as those patentsmentioned above. Upon subsequent chlorination, phenols treated in such amanner show a reduction in the typical dark reddish or brownish colorwhich chlorination usually imparts to pentachlorophenol made fromphenols produced by the cumene process or sulfonation of benzene.

However, such phenol purification techniques suffer from thedisadvantages of elaborate and costly equipment and procedure. In otherwords, in order to obtain a polychlorinated phenol such aspentachlorophenol free from colored impurities, heretofore it wasnecessary to perform a special purification on phenol already purifiedto U.S.P. grade, recover the phenol from such a special process,chlorinate the phenol and then recover the chlorinated phenol.

An improved process for the manufacture of polychlorinated phenols ofimproved (i.e., lighter) color is disclosed in a copending U.S. PatentApplication assigned to the assignee of the present invention. Astherein disclosed, chlorination of the phenol starting material isperformed to obtain a mixture of chlorophenols containing from 1 to 3chlorine atoms per molecule of phenol, at least 40 percent of thechlorinated phenol mixture being in the form of dichlorophenols. Thereaction mixture is thereafter distilled to separate a lightcoloredchlorophenol distillate from a residue containing dark color-formingimpurities, and the distillate may be further chlorinated to formpentachlorophenol.

Certain impurities such as the chlorodibenzo-pdioxins (commonly known aschlorodioxins) generally present in chlorinated phenols may be toxic tohumans, possibly even in the low concentrations, e.g., about 2,000p.p.m., present in technical grade pentachlorophenol. These chlorodioxinimpuritiesare apparently formed during phenol chlorination and are thusnot removed during special phenol purification procedures prior tochlorination. If the safety hazard of these compounds is established,then the removal of chlorodioxin to a safe level (i.e., below about 100p.p.m.) will be necessary.

PRODUCTION OBJECTS AND SUMMARY OF THE INVENTION It is an object of thepresent invention to produce chlorinated phenols of light color by aprocess which obviates or substantially alleviates the problems anddrawbacks associated with prior art techniques.

It is another object of the present invention to produce essentiallycolor-free polychlorinated phenols such as pentachlorophenol without anyelaborate purification of the phenol.

Still another object is to reduce the chlorodioxin content ofpentachlorophenol while also removing colorproducing impurities.

These and other objects as well as the manner of achieving them willbecome apparent to those skilled in the art from the detaileddescription which follows.

The present invention provides a method for the separation and recoveryof polychlorinated phenol from dark color-forming impurities containedtherein comprising the steps of:

a. introducing into a distill and mixture of at least onepolychlorinated phenol and dark color-forming impurities, an amounteffective to inhibit color formation of at least one color inhibitorselected from the group consisting of zinc dust and free radical-actingsubstances;

b. distilling the resulting color inhibitor containing distilland toseparate polychlorinated phenol vapors therefrom; and

c. condensing said vapor to recover purified polychlorinated phenols.

In the absence of a contrary indication, all proportions and percentagesof materials are expressed in this specification on a weight basis.

DESCRIPTION OF PREFERRED EMBODIMENTS Although the process of the presentinvention may advantageously be performed on any chlorinated phenol,regardless of the method of manufacturing the chlorinated phenol, it hasbeen found that the present process is particularly applicable to theremoval of dark color-forming impurities from pentachlorophenol.

The pentachlorophenol which may be treated according to the presentinvention may be produced in any suitable manner. Generally,pentachlorophenol is produced by the chlorination of phenol or byhydrolysis of hexachlorobenzene. Although either method is acceptableand both methods are known in the art, production of pentachlorophenolby the chlorination of phenol is preferred.

The phenol starting material, which may be chlorinated to formthechlorinated phenols, may be produced by the decomposition of cumenehydroperoxide of by sulfonation of benzene. Even when purified to adegree which satisfies U.S.P. requirements, such phenol still containstraces of color-forming impurities which cannot be separated bydistillation or other conventional methods. Chlorinated phenols derivedfrom phenol made by the above mentioned processes are significantlyimproved in color by the process of the present invention.

When cumene process phenol is used as the starting material, it .ispreferred to use the phenol after it has been treated, for example, byfractional distillation of the washed and neutralized cumenehydroperoxide decomposition reaction product. Such a treatment removesmost of the lower boiling materials such as acetone, cumene,alpha-methylstyrene and most of the higher boiling materials such asacetophenone and phenyl dimethylcarbinol, although a residual quantity,e.g., up to about 0.1 percent based on phenol, of any or all of theseimpurities may remain in the phenol fraction.

Chlorination may be conducted in any convenient manner known.Chlorination processes are shown, for example, in US. Pat. Nos.2,131,259 and 2,947,790, the specifications of which are both hereinincorporated by reference.

Typically, in these known processes, the phenol starting material isreacted at a temperature at the start of the chlorination in the rangeof 65C. to 130C. (preferably about 100C to l C) and is held at this tenrperature until the melting point of the product is 95C and about 3 to 4atoms of chlorine are combined as determined by analysis, at which timethe temperature is progressively increased to maintain a preferreddifferential temperature of 10C. over the product melting point.

The chlorination process is carried out at substantially atmosphericpressure for a time of from about 5 to about hours. The chlorinationreaction may be carried out in the liquid phase in the absence of anyadded solvents and in the presence of aluminum chloride catalyst. Thecatalyst concentration in these known chlorination processes ismaintained below 0.0085 mol of anhydrous aluminum chloride per mol ofphenol, preferably not more than 0.075 mol and not less than 0.004 molof anhydrous aluminum chloride per mol of phenol. The initialchlorination up to where 2 to 2.7 atoms of chlorine are combined per molof phenol may be carried out in the absence of catalyst.

Pentachlorophenol production by hydrolysis of hexachlorobenzene is alsowell-known and is shown, for example, in US. Pat. Nos. 2,107,650 and2,812,366.

An efficacious chlorination process for the production ofpentachlorophenol is disclosed in the aforementioned copending US.Patent Application which discloses chlorination of the phenol startingmaterial to obtain a mixture of chlorophenols containing from 1 to 3chlorine atoms per molecule of phenol, at least 40 percent of thechlorinated phenol mixutre being in the form of dichlorophenols. Thereaction mixture is thereafter distilled to separate a light-coloredchlorophenol distillate from a residue containing dark color-formingimpurities, and the distillate may be further chlorinated to formpentachlorophenol.

Generally, all of the above noted processes yield technical grade"pentachlorophenol. In addition, and regardless of the method ofproduction, technical grade pentachlorophenol is a commerciallyavailable product. Technical grade pentachlorophenol is a generallybrownish-colored solid which contains from about 86 to 95 percentpentachlorophenol, about 2 to 10 percent tctrachlorophcnol and up toabout 4 percent of other compounds, most of which are unidentified. Asnoted before, technical grade pentachlorophenol generally also containsabout 1,800 to 2,400, generally of zinc dust and free radical-actingsubstances to separate pentachlorophenol vapor therefrom and condensingsaid vapor to recover purified pentachlorophenol. Ethylene thiourea orzinc dust appear to offer an optimum combination of improved productcolor, process efficiency and cost and are therefore the preferred colorinhibitors.

The free radical-acting color inhibitors can be any free radical-actingsubstances which provide improved color properties and removecolor-forming impurities from the pentachlorophenol during distillation.Typi cally, suitable free radical-acting color inhibitors include freeradical-acting compounds of the phenol. hydroquinone, organic sulfurderivative, organic phosphite, amine or aldehyde type.

Phenol compounds, for example, which have been found suitable for use inthe present invention include 2,6-ditertiary butyl eresol, alphanaphthol, paminophenol, 4-(methylthio)phenol, 2,2-methylenebis(4-methyl-6-tert-butyl phenol), Plastanox l 161, a hinderedphenol commercially available from the American Cyanamid Co.,2,2-methylenebis(4- ethyl-6-terbutyl phenol) and p-tertiary butylcatechol.

Suitable hydroquinone compounds include hydroquinone, 2,5ditertiarybutyl hydroquinone, monotertiary butyl hydroquinone and monomethyl etherof hydroquinone.

Organic sulfur derivatives which have been found suitable include alkylphenol disulfide commercially available as Vultac No. 3 from thePennwalt Company; ethylene thiourea, mixed thioureas commerciallyavailable as Pennzone L from the Pennwalt Company; liquiddithiocarbamatc commercially available as Merac No. 255 from thePennwalt Company; ditridecylthiodipropionate, anddistearylthiodipropionate.

Suitable organic phosphites include trinonyl phosphite, tris-2(chloroethyl)-phosphite, and triisooctyl phosphite.

Amines which have been found suitable include N,N--bis(1,4-dimethylpentyl)-p-phenylene diaminc while suitable aldehydesinclude salicylaldehyde.

The color inhibitor is added to the impuritycontaining pentachlorophenolin an amount effective to inhibit color formation, which amount isgenerally in the range of from about 0.02 to about 2, preferably fromabout 0.1 to about 0.5 percent by weight of the starting material.

The term free radical-acting substance" is intended to include thosecompounds such as described above which function as scavengers for theimpurities in the polychlorinatcd phenol.

Although the mechanisms of reaction are unclear and 1 do not wish to bebound by theoretical considerations, it would appear that the colorinhibitors react with the color-imparting impurities in the crude pentachlorophenol to render them separable on distillation.

A conventional vacuum flask evaporator is satisfactory to carry out thedistillation. For example, the distillation apparatus may be a vacuumbatch still with heat being supplied to the still by a forcedcirculation reboiler heated with circulating hot oil. Vapors pass outthe top of the batch pot through a column containing side-toside traysand are condensed in a shell and tube type condenser (vapor on theinside of the tubes and high pressure steam generated on the outside). Areduced pressure is maintained on the system by a dual stage jet ejectorin manner well known in the art.

about 160 or more mm. Hg, preferably from about 35 to about 150 mm. Hg,and at a temperature of from about 185C. to 235C., preferably from about195C. to about 220C. Distillation may be continued to achieve from about84-percent to 96 percent, often from about 90 percent to 96 percent.distillate recovery with good results.

When the distillation is carried out under the condi tions noted above,the distillate comes over essentially water-white in color, while theresidue remains as a dark liquid. That is, a weight percent sample ofthe distillate in Xylene generally yields a transmission value using alight having a wavelength of 475 mp. and a light path of 10 mm. of fromabout 95 to about 100 percent of the value of a water-white xylenereference standard. The chlorodioxin content of the essentiallywater-white colored distillate is generally below about 25 p.p.m.

Pentachlorophenol is used in the preservation and treatment of wood. Incertain applications (fence poles, housing substructures),pentachlorophenol color is relatively unimportant. In many other uses inthe woodworking industry, particularly where painting of the treatedproduct is necessary, a light or water-white colored pentachlorophenolis highly desirable.

The invention is additionally illustrated in connection with thefollowing examples which are to be considered as illustrative of thepresent invention. It should be understood, however, that the inventionis not limited to the specific details of the Examples.

EXAMPLE I Distilled pentachlorphcnol was obtained from equipment of twosizes. The smaller reactor consisted of a glass tube in a temperaturecontrolled aluminum block. A charge of 5 parts by weight impurepentachlorophenol was placed in a heated zone and distilled or sublimedinto a cool zone outside the block. The reactor was equipped with atemperature controller, manostat, traps and vacuum gauge and pump. Thelarger reactor contained a 500 parts by weight impure pentachlorophenolcharge in a semi-spherical glass vessel equipped with a short Vigreauxtube, condenser, receiver, and

the usual vacuum equipment as with the smaller reactor. The reactor washeated by a molten salt bath.

The starting material for each run was commercially available technicalgrade pentaehlorophenol. This maidentified.

In each run, the indicated amounts of impure pentachlorophenol and colorinhibitor are charged to the reactor and the mixed charge heated to theindicated temperature under the indicated pressure. Color of theresulting distillate is determined visually and by measuring thetransmittance of a light 475 mp. through a 1 cm. Pyrex glass cell with alight path of 10 mm. containing 10 weight percent of pentachlorophenolproduct in xylene. A matching cell of the water-white xylene is used asa reference standard and is assigned a value of 100 percenttransmission.

The run conditions utilized and results obtained are shown below inTable I.

TABLE 1 Run Conditions Results Sample Size, Color of Chloro- Partslnhih- Temp- Charge dibenzo- Trans- Visual by itor, Pressure eratureDisp-dioxins mittance Color of Color Inhibitor Type Weight '7: mm Hg C.tilled ppm Solid Comments Control distilled no 500 none 150 246 85.6 9190.2 yellow inhibitor 500 134 244 92,6 61 91.4 500 51 213 25 8644Phenols hydroquinones 2,6-Ditertiary butyl cresol (Shell lonol) 500 0.51 214 ND* 96.5 white 5 0.1 3 198 100.0 2.5-Ditertiary hutylhydroquinone 500 1.0 125 235 N1) 97.2 5 1.0 36 198 98.5 Hydroquinone 50.1 198 16 98.7 Monotertiary huty1hydro quinonc 5 1.0 35 198 99.5 AlphaNaphthol 5 0.1 36 198 100.0 p-Aminophenol 5 1.0 36 198 53.04-(Methylthio)phcnol 5 1.0 36 198 100.0 Monomethyl ether of hydroquinonc5 1.0 36 198 100.0 2.2'-Methy1ene bis(4- methyl-6-tert-hutyl phenol)[Plastanox 2246]" 5 0.1 36 198 94.8 500 0 25 47 215 92.0 ND 97.0Hindered phenol [Plastanox 1161]- 5 0.5 36 198 99.5 2,2Meth \'1cnehis(4- ethyl-6-tert-but \'l phenol) [Plastanox 425]" 5 0.1 36 198 100.0p-Tertiary hutyl catcchol 5 0.1 36 198 98.8 Alkyl phenol disulfidc[Vultac No. 3]" 500 0 5 49 218 ND 98.0 Sulfur compounds Ethylenethiourea 5 1.0 36 198 94.8 white 500 0. 50 214 30 97.9 Mixed thioureas(Pennzone 1.) 500 0.25 50 214 ND 96.0 Liquid dithiocarhamate (Merac No.255)" 500 0,25 48 214 92.0 90. Ditridecylthiodipropionate [Plastanox711]" 5 1.0 36 198 99.4 500 0 1 50 215 :25 98.0

TABLE 1 -Continued Run Conditions Results Sample Size. Color "/1 ofChlord- Parts Inhih- Tcmp- Charge dibenzo- Trans- Visual hy itor.Pressure erature Disp-dioxins mittance Color of Color Inhibitor TypeWeight 7: mm Hg C. tilled ppm 7: Solid Comments Distearylthiodipropionate [Pl-.tstanox STDPI" 5 ().I7 36 I98 99.0 Alkylphosphites Trinonyl phosphitc (Uvi-Nox 3 I)" [.0 36 I98 99.0 500 0.2 502I5 90.0 ND 98.8 Tris-2(chloroethyl)- phosphite 500 0.5 I10 237 74.4 ND94.1 Triisooctyl phosphite 5 1.0 36 I98 89.4 23

500 I .0 65-150 I 80-23 I 92.6 97.0 white Amines and Aldehydes, AcidsMiscellaneous Salicylaldehyde 5 L0 36 I98 96.5 It. yellow N,N-his(I,4-dimeth vl- Solution pentyI)-p-phenylene clear and diamine [Tenamine4] 5 I.() 36 I98 81.2 white It. purple 500 0.25 48 7 I4 93.0 ND 98.

Metals Zinc dust 500 0.35 50 2I5 890 100.0 white *None detected ShellChemical Corporation American Cyanamid Company "GAF Corporation"Pennwalt Corporation 'Eastman Chemical Products. Inc.

These runs show that various color inhibitor compounds in varyingamounts are effective to remove all or substantially all of the darkcolor-forming impurities under vacuum distillation conditions. Colorimprovements was performed with the recovery of substantially all of theoriginal charge. Both visual color and transmittance of the samples arevery good (i.e.. generally white color and 95 percent or bettertransmittance) regardless of sample size or amount of inhibitor. In addition, the amount of chlorodioxins is substantially reduced (i.e., below25 p.p.m.). Apparently some of the p-aminophenol andN,N-bis(l,4-dimethylpentyl)-pethylene diamine tetraacetic acid, oxalicacid, iron powder, sodium meta bisulfite. sodium borohydride andstannous oxalate. The conditions and results obtained are shown below inTable II. Generally, the pentachlorophenol distilled containing thesecompounds had unsatisfactory color (yellow). While the sodiumborohydride run yielded good transmittance and visual color values, theheel or residue of undistilled charge was generally larger (and thepercent of charge distilled was therefore generally smaller) thanrealized with the color inhibitors of the present invention. Other runswith sodium borohydride indicate that relatively large 40 phenylenedtamtne eolormhtbitors distilled over during amounts of the materialmust be used to achieve acthe run which caused the transmittance of theresulting ceptable color improvement. These runs also indicate,distillate samples to be below that obtained with the however, that thepercent of charge distilled decreases other color inhibitor materials.with increasing amounts of sodium borohydride and COMPARATIVE EXAMPLEthat values of only about to percent of the charge Example I is repeatedutilizing dimethyl sulfoxide. distilled are often realized.

TABLE 2 Run Conditions Results Sample Size, Color 71 of Chloro- Partslnhib- Temp- Charge dibenzo- Trans- Visual by itor. Pressure eratureDisp-dioxins mittance Color of Color Inhibitor Type Weight 7! mm Hg C.tilled ppm "/1 Solid Comments Amines and Aldchydes, Acids MiscellaneousDimethyl sulfoxide 5 ".0 36 I98 98.0 It. yellow Ethylene diaminetetraacetic acid 5 L0 36 I98 94.8 Solution Oxalic acid 5 H) 36 I98 83.2contains suspended precipitatc & is It. yellow Metals and InorganicCompounds Iron powder 5 1.0 36 I98 94.2 yellow Sodium meta bisullite 5I.0 36 I98 95.0 Stannous oxalate 5 2.0 36 I98 942 5 02s 36 198 83.6 987white Sodium borohydride The principles, preferred embodiments and modesof operation of the present invention have been described in theforegoing specification. The invention which is intended to be protectedherein, however. is not to be construed as limited to the particularforms disclosed, since these are to be regarded as illustrative ratherthan restrictive. Variations and changes may be made by those skilled inthe art without departing from the spirit of the invention.

b. distilling the resulting color inhibitor containing distilland at apressure of from about 35 to about mm. Hg and at a temperature of aboutC. to about 220C. to separate pentachlorophenol vapors therefrom and c.condensing said vapor to recover purified pentachlorophenol in an amountof at least 84 percent of the impurity-containing pentachlorophenol.

2. The method of claim 1 wherein said impure pentachlorophenol containschlorodioxins and the purified pentachlorophenol contains lower amountsof chlorodioxins.

3. The process of claim 1 wherein said impure pentachlorophenol istechnical grade pentachlorophenol produced by the chlorination ofphenol.

4. The process of claim 3 wherein said phenol is produced by thedecomposition of cumene hydroperoxide.

5. The process of claim 3 wherein said phenol is produced by thesulfonation of benzene.

1. A METHOD FOR THE SEPARATION AND RECOVERY OF PENTACHLOROPHENOL FROM DARK COLOR-FORMING IMPURITIES CONTAINED THEREIN COMPRISING THE STEPS OF, A. INTRODUCING INTO A DISTILLAND MIXTUREOF PENTACHLOROPHENOL AND DARK COLOR-FORMING IMPURITIES AN EFFECTIVE AMOUNT OF FROM ABOUT 0.1 TO ABOUT 0.5 PERCENT BY WEIGHT OF THE IMPURITY-CONTAINING PENTACHLOROPHENOL OF A ZOLOR INHIBITOR OF ZINC DUST OR ETHYLENE THIOUREA, B. DISTILLINGTHE RESULTING COLOR INHIBITORCONTAINING DISTILLAND AT A PRESSURE FROM ABOUT 35 TO ABOUT 150 MM. HG AND AT A TEMPERATURE OF ABOUT 195*C. TO ABOUT 220*C. TO SEPARATE PENTACHLOROPHENOL VAPORS THEREFROM AND C. CONDENSING SAID VAPOR TO RECOVER PURIFIED PENTACHLORPHENOL IN AN AMOUNT OF AT LEAST 84 PERCENT OF THE IMPURITY-CONTAINING PENTACHLOROPHENOL.
 2. The method of claim 1 wherein said impure pentachlorophenol contains chlorodioxins and the purified pentachlorophenol contains lower amounts of chlorodioxins.
 3. The process of claim 1 wherein said impure pentachlorophenol is technical grade pentachlorophenol produced by the chlorination of phenol.
 4. The process of claim 3 wherein said phenol is produced by the decomposition of cumene hydroperoxide.
 5. The process of claim 3 wherein said phenol is produced by the sulfonation of benzene. 